Heat exchanger and method

ABSTRACT

A shell and tube heat exchanger includes a plurality of tubes having non-circular cross sectional shapes to improve heat transfer. The tubes may have central portions having an oblong cross-sectional shape with generally flat opposite side faces. The side faces may include raised portions to increase heat transfer. Alternatively, the tubes may have a C-shape in cross section. The shape of the tubes promotes thin film boiling of the fluid in the tubes to improve heat transfer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/738,080 filed on Dec. 17, 2012, entitled, “HEAT EXCHANGER AND METHOD”, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Various types of shell and tube heat exchangers have been developed. Known heat exchangers may include a shell having fluid inlets and outlets to provide for circulation of fluid through the shell. A plurality of smaller tubes are disposed within the shell. The smaller tubes have inlets and outlets disposed outside the shell whereby fluid can flow through the tubes. Heat is thereby exchanged between the fluid flowing through the shell and the fluid flowing through the tubes.

With reference to FIG. 1, a known shell and tube heat exchanger construction may include an inner assembly comprising a plurality of tubes 1 having opposite ends 2 and 3 that are connected to end plates 4 and 5, respectively, at openings 7 and 8. O rings 6 may be utilized to seal the ends 2 and 3 to openings 7 and 8, in end plates 4 and 5. A solid rod 9 may be positioned inside each tube 1 to create an annular space 10 between the solid rod 9 and the tubes 1. The tube assembly of FIG. 1 is positioned inside a shell (not shown) when the heat exchanger is fully assembled. In use, fluid flows through the small annular space 10 to thereby transfer heat between fluid flowing through tubes 1 and the fluid flowing through the shell (not shown). U.S. Pat. Nos. 7,785,448 and 8,069,676 also disclose heat exchangers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially exploded isometric view of a portion of a prior art heat exchanger;

FIG. 2 is a cross sectional view of a heat exchanger according to one aspect of the present invention;

FIG. 3 is a cross sectional view of the heat exchanger of FIG. 1 taken at an orientation that is rotated 90° relative to the orientation of FIG. 1;

FIG. 4 is a cross sectional view of the heat exchanger of FIG. 3 taken along the line IV-IV;

FIG. 5 is a partially schematic view of a tube being formed according to one aspect of the present invention;

FIG. 6 is a view of a tube that has been deformed according to one aspect of the present invention;

FIG. 6A is an enlarged end view of the tube of FIG. 6;

FIG. 7 is a view of a tube that has been deformed according to another aspect of the present invention;

FIG. 7A is an enlarged end view of the tube of FIG. 7;

FIG. 8 is a flattened tube according to another aspect of the present invention;

FIG. 8A is an enlarged end view of the tube of FIG. 8;

FIG. 9 is an isometric view of the tube of FIGS. 6 and 7;

FIG. 10 is an isometric view of a subassembly of a heat exchanger including flattened tubes that have been connected to a pair of end plates;

FIG. 11 is a cross sectional view of a heat exchanger according to another aspect of the present invention;

FIG. 12 is a cross sectional view of the heat exchanger of FIG. 11 taken along the line XII-XII;

FIG. 13 is a cross sectional view of the heat exchanger of FIG. 11 taken along the line XIII-XIII;

FIG. 14 is a fragmentary view of a tube for the heat exchanger of FIG. 11, wherein the tube is C-shaped in cross section;

FIG. 15 is an enlarged end view of an extruded version of the tube of FIG. 14;

FIG. 16 is an enlarged end view of a version of the tube of FIG. 14 wherein the tube is formed from sheet metal;

FIG. 17 is an enlarged view of a portion of the tube of FIG. 16 during the forming process;

FIG. 18 is an enlarged view of a portion of the tube of FIG. 16 showing the final deformed shape of the sheet metal utilized to form the tube; and

FIG. 19 is a fragmentary isometric view of the tube of FIG. 14.

DETAILED DESCRIPTION

With reference to FIGS. 2 and 3, a heat exchanger 15 according to one aspect of the present invention includes a shell 16 and a tube assembly 18 disposed in a cavity 20 of shell 16. An inlet 22 receives super heated steam or vapor “A” (FIG. 2) that flows across boiler tubes 24. The steam or vapor condenses inside shell 16 due to cooling provided by tubes 24, and the water flows out of an exit 26 of shell 16 in the form of distilled liquid water 28.

The tube assembly 18 includes a plurality of boiler tubes 24 having opposite ends 30 and 32 that are connected to end plates 34 and 36, respectively. End plate 36 is fluidly connected to a fluid inlet 38 that receives inlet or tap water 40. The water 40 flows upwardly through the boiler tubes 24, and enters space 42 above plate 34 in the form of steam or vapor. The steam/vapor 46 exits space 42, and flows to a blower or compressor (not shown). Waste water and particulate matter 48 flows out of an outlet 50 of shell 16. The heat exchanger 15 may include a flow straightener 52 positioned on or adjacent plate 36 to direct the flow of water from inlet 38 through end plate 36 into tubes 24. As discussed in more detail below, tubes 24 include end portions 54 having a circular cross sectional shape enabling the ends to be connected to circular openings 56 in end plates 34 and 36. The tubes 24 also include flattened central portions 58 forming an elongated/flat passageway 60 to promote heat transfer between fluid flowing through tubes 24 and fluid flowing through cavity 20 of shell 16. As discussed in more detail below, the tubes 24 provide increased heat transfer, such that the length “L” of the tubes 24 and length “L1” of the heat exchanger 15 can be significantly reduced relative to known configurations.

During fabrication (FIG. 5), a tube 12 having a circular cross sectional shape with generally uniform wall thickness is flattened utilizing die or forming members 14 to thereby form flattened central portion 58. End plugs 62 include cylindrical portions 64 that are closely received in open ends 66 of tube 12 immediately prior to forming by forming members 14. The cylindrical portions 64 remain inserted in the open ends 66 of tube 12 as forming members 14 deform the tube 12 to thereby insure that the ends 154 of tubes 12 retain a circular cross-sectional shape.

Referring to FIGS. 6, 6A, 7, and 7A the side walls 68 of flattened central portion 58 may be substantially flat, or the side walls 68 may include a plurality of elongated raised portions 70 that further increase the surface area of flattened central portion 58. It will be understood that the flattened central portion 58 may be formed in more than one step utilizing a series of forming members or dies 14 as required for a particular application. Also, a forming member or fluidic materials such as oil or semi-fluidic materials such as sand or iron filings (not shown) may be inserted into flattened portion 58 of tube 12 following an initial forming step to thereby facilitate additional forming steps to form elongated raised portions 70. The tubes 24 include a transition zone or portion 72 having a shape that transitions between the flattened central portion 58 and the end portions 54. The wall thickness of the tube following the forming process is preferably uniform or approximately uniform.

With further reference to FIG. 8, a tube 24A according to another aspect of the present invention includes a flattened central portion 58A having a plurality of raised portions 74 that increase the surface area of side walls 68A of tube 24A. Raised portions 74 may have a dome-like shape, with a generally uniform wall thickness in the raised portions 74 and surrounding planar portions. Tube 24A may be formed in substantially the same manner as tube 24, and includes circular ends 54 that can be connected to end plates 34 and 36.

With further reference to FIGS. 9 and 10, end plates 34 and 36 include a plurality of circular openings 76. The openings 76 may be formed by punching, extruding, or other suitable process, and may be flared to provide increased surface area in the vicinity of the joint formed with ends 54 of tubes 24. During assembly, ends 54 of boiler tubes 24 are inserted into the circular openings 76 of end plates 34 and 36 and secured thereto to form a subassembly 80. The ends 54 of tubes 24 may be flared outwardly or otherwise formed utilizing a “bullet” (not shown) or other suitable forming operation to thereby secure ends 54 of tubes 24 to end plates 34 and 36. The ends 54 may also be soldered or brazed at the joints where ends 54 of tubes 24 connect with end plates 34 and 36.

It will be understood that the flattened central portions 58 may, in some cases, be formed after the tubes 12 are connected to the end plates 34 and 36. For example, the ends 54 of a tube 12 may be positioned in openings 76, and a single forming member or “bullet” may be drawn or pushed through the length of tube 12 to thereby expand the tube 12 along its entire length. This expansion causes a tight mechanical fit between ends 54 of a tube 12 and end plates 34 and 36. Soldering or brazing may also be utilized to secure the joints between tubes 12 and end plates 34 and 36. The individual tubes 12 may then be flattened utilizing forming members or dies 14 after the tubes 12 are connected to the end plates 34 and 36.

In FIG. 10, end plates 34 and 36 have a rectangular perimeter. However, end plates 34 and 36 may also have a circular perimeter that corresponds to the circular cross-sectional shape of shell 16 as shown in FIG. 4. Also, shell 16 (FIGS. 2-4) may have a square or rectangular cross-sectional shape, and end plates 34 and 36 may have corresponding rectangular perimeters.

The boiler tubes 24 may be formed of copper, aluminum, or other suitable material. If the tubes 12 comprise aluminum or other material that degrades when exposed to heat, steam, boiling water, etc., the tubes 24 may be coated with an epoxy material or other suitable coating to insure that the tubes 24 can withstand the adverse conditions experienced during operation of heat exchanger 15.

After subassembly 80 (FIG. 10) is formed, the shell 16 (FIGS. 2-4), inlet and outlet fittings, and other components may be assembled with the subassembly 80 utilizing known processes.

The flattened central portions 58 of tubes 24 promote thin film boiling of water passing through the tubes 24 to thereby provide for efficient transfer of heat between fluid passing through tubes 24 and fluid circulating through cavity 20 of shell 16. The passageways 60 formed by flattened central portions 58 have an oblong cross sectional shape with an internal dimension of about 0.2 by about 1.5 inches. It will be understood that the specific dimensions of the flattened portions 58 of tubes 24 and the internal passageways 60 may vary depending upon the requirements of a particular application. In contrast to known tubes with internal rods (e.g. FIG. 1), heat is transferred to/from internal passageways 60 on the two elongated sides of the extended perimeter oval profile (i.e. through both side walls 68) rather than the shorter perimeter of the circular profile.

With further reference to FIGS. 11-13, a heat exchanger 15A according to another aspect of the present invention includes a shell 16A that is substantially similar to the shell 16 described in more detail above in connection with FIGS. 2-4. Heat exchanger 15A includes a plurality of tubes 24A (see also FIGS. 14-19). Each tube 24A has a substantially C-shaped cross section. Tubes 24A include cylindrical concave inner surface portions 82 and convex outer cylindrical surface portions 84, and an elongated internal passageway 86. Internal passageway 86 is generally C-shaped. In the illustrated example, passageway 86 is preferably about 0.2 inches between inner and outer side walls 88 and 90, and about 2.0 inches long, such that the cross-sectional area of passageway 86 is about 0.4 square inches.

Tubes 24A may be formed from extruded aluminum or other suitable material as shown in FIG. 15. Extruded tube 24A may include integral transverse inner walls 89 defining three internal passageways 86A, 86B, and 86C.

Alternatively, tubes 24A may be formed from sheet metal or the like as shown in FIG. 16. The sheet metal may have a bend or fold forming a curved edge 96 interconnecting formed/curved inner and outer side wall portions 88 and 90. As shown in FIG. 17, an edge portion 92 (FIG. 17) of side wall 88 may then be deformed to bring it into contact with edge portion 94. The edge portion 94 of side wall 90 may then be folded/formed to form an elongated sealed joint 98 as shown in FIG. 18.

The folding operations of FIGS. 17 and 18 utilized to form sealed joint 98 may comprise high speed forming that causes the end portions 94 and 96 of side walls 88 and 90 to become fused together due to melting/bonding of the edges 92 and 94. High speed forming of this type is generally known, such that the details of this process will not be described in detail herein. Alternatively, the edge portions 92 and 94 may be deformed utilizing rollers or other forming tools, and the joint 98 may then be sealed utilizing solder, brazing, epoxy, or the like.

The tubes 24A form elongated passageways 86A, 86B, and 86C (FIG. 15) or 86

(FIG. 16) that are somewhat similar to an annular shape, except that the internal passageways 86 are generally C-shaped as a result of the tubes 24A being formed by extrusion (FIG. 15) or from a single piece of sheet metal (FIGS. 16-18) (in contrast to the known tubes 1 and solid rods 9 of FIG. 1) having a cylindrical outer surface of the same radius as outer wall 90. Also, the surface areas of external surfaces of inner wall 88 and outer wall 90 are significantly larger than the cylindrical outer surface of a conventional tube (e.g. FIG. 1), and provide for heat transfer on both sides of passageways 86. The increased surface area provides increased heat transfer between fluid inside tubes 24A and fluid in shell 16A relative to conventional tubes (FIG. 1).

End plates 34A and 36A of heat exchanger 15 (FIGS. 11-13) may include C-shaped openings to closely receive the ends 54A of tubes 24A. Ends 54A of tubes 24A may be secured to end plates 34A and 36A by forming ends 54A, or by utilizing epoxy, solder, brazing, or the like to provide a secure, sealed bond between tubes 24A and end plates 34A and 36A.

The transfer of heat into passageway 86 (or passageways 86A, 86B, and 86C) through side walls 88 and 90 on both sides of the internal passageways 86 promotes thin film boiling of water flowing through tubes 24A. This increases heat transfer between material flowing through tubes 24A and fluid flowing through shell 16A of heat exchanger 15A. Similarly, heat is transferred through both side walls 68 of tubes 24 (FIGS. 2-10) on both sides of passageways 60 to promote thin film boiling of water or other fluid in passageways 60. Because the heat transfer is improved, the length L (FIGS. 2, 10, and 11) of tubes 24 and 24A can be significantly reduced compared to known heat exchangers utilizing round tubes or round tubes with internal rods (e.g. FIG. 1). The length L1 of the heat exchanger (FIGS. 2 and 11) can therefore also be reduced significantly. In general, for a given heat transfer capability the lengths L and L1 can be reduced by 10%-20% or more relative to a conventional arrangement (FIG. 1).

As discussed above, the tubes 24 and 24A, and end plates 34, 36, 34A, and 36A may be formed from a suitable metal material such as copper or aluminum. Alternatively, one or more of these components may be formed from polymer materials having the required strength and durability required to withstand the operating conditions of the heat exchangers 15, 15A.

A heat exchanger according to the present invention as described above in connection with FIGS. 1-19 may be utilized in a wide variety of applications. For example, the inventive heat exchanger may be utilized as an evaporator and/or a condenser in refrigeration systems. It will be understood that the shape, size, and number of tubes and other components may vary according to the requirements of a particular application. 

The invention claimed is:
 1. A heat exchanger, comprising: a shell defining a cavity and including fluid inlets and outlets to permit flow of a first fluid through the cavity; an inner tube assembly comprising at least one elongated tube and fluid conduits connected to opposite ends of the tube, the fluid conduits extending outside the shell to permit flow of a second fluid through the inner tube assembly; and wherein: the at least one tube includes an elongated internal passageway, wherein at least a portion of the elongated internal passageway of the tube has an oblong shape in cross section to promote thin film boiling of fluid flowing through the elongated internal passageway to thereby provide increased heat transfer from the first fluid to the second fluid.
 2. The heat exchanger of claim 1, wherein: the tube comprises a plurality of tubes having elongated internal passageways, wherein at least a portion of the elongated passageways have oblong shapes in cross section.
 3. The heat exchanger of claim 2, wherein: each tube has opposite ends, each opposite end defining a substantially circular opening.
 4. The heat exchanger of claim 3, wherein: each tube includes transition sections extending between the substantially circular openings and the portion of each tube having an oblong shape in cross section.
 5. The heat exchanger of claim 4, wherein: each tube includes an elongated central portion having an oblong cross sectional shape.
 6. The heat exchanger of claim 5, wherein: the elongated central portion of each tube includes a pair of generally planar side wall portions that are spaced apart, and a pair of curved sidewall end portions interconnecting the generally planar side wall portions.
 7. The heat exchanger of claim 6, wherein: the generally planar side wall portions have a substantially uniform thickness.
 8. The heat exchanger of claim 7, wherein: at least a portion of each generally planar side wall portion includes a plurality of raised portions forming protrusions on outer surfaces of each generally planar side wall portion.
 9. The heat exchanger of claim 8, wherein: the protrusions comprise elongated ridges extending along the tubes.
 10. The heat exchanger of claim 8, wherein: the protrusions comprise a plurality of generally circular bulges.
 11. The heat exchanger of claim 1, wherein: the at least one tube comprises sheet metal having a substantially uniform thickness.
 12. A tube assembly for a shell and tube heat exchanger, the tube assembly comprising: first and second end plates having a plurality of generally circular openings therethrough; a plurality of tubes extending between the first and second end plates, each tube having opposite end portions with outer surfaces that have a generally circular cross sectional shape, wherein the opposite end portions are received in the openings of the first and second end plates and being connected thereto; and wherein: the tubes have flattened central portions forming fluid passageways having oblong cross sectional shapes to thereby provide improved heat transfer.
 13. The tube assembly of claim 12, wherein: the flattened central portions of each tube includes a pair of spaced apart side wall portions that are generally planar.
 14. The tube assembly of claim 13, wherein: each tube includes curved side wall portions extending between and interconnecting the generally planar side wall portions.
 15. The tube assembly of claim 13, wherein: the generally planar side wall portions include a plurality of raised portions forming protrusions on outer surfaces of each generally planar side wall portion.
 16. The heat exchanger of claim 15, wherein: the protrusions comprise elongated ridges extending along the tubes.
 17. The heat exchanger of claim 15, wherein: the protrusions comprise a plurality of generally circular bulges.
 18. A tube for shell and tube heat exchangers, the tube comprising: an elongated tubular structure having spaced apart inner and outer side walls that are generally C-shaped in cross section, wherein the inner and outer side walls are interconnected by transverse end wall portions to form an internal passageway that is generally C-shaped.
 19. The tube of claim 18, wherein: the inner and outer side walls define outer surfaces that are generally cylindrical in shape.
 20. The tube of claim 18, wherein: the tube comprises sheet metal having elongated opposite edge portions that are interconnected to form a tube.
 21. The tube of claim 20, wherein: the opposite edge portions are interconnected by folds to form a first transverse end wall portion.
 22. The tube of claim 21, wherein: the tube comprises a single piece of sheet metal that is deformed to define a second transverse end wall portion. 